The research proposed is directed at elucidation of the mechanisms of action of the glutathione S-transferases in the chemical nd physical disposition of toxic xenobiotics. Four areas of investigation are proposed including: (1) the stereochemical mapping or the topology of the active site of the enzyme with specifically designed and toxicologically relevant substrates; (2) the synthesis and use of peptide substrate analogs to determine the structural requirements for recognition of glutathione by the enzyme; (3) the determination of the kinetic and chemical mechanisms of catalysis including identification of essential active site functional groups; and (4) an investigation of the role of glutathione S-transferase as an intracellular xenobiotic transport protein. Stereo- and enantioselectivity of the enzyme toward arene oxide and Beta-lactone substrates will be used to determine active site topology of the enzyme. Glutathione substrate analogs including retro-glutathione, glutathione diastereomers, and methylene homologs will aid in determining the structure of the glutathione binding site. The structure of the active sites of the glutathione S-transferase isozymes together with a knowledge of their kinetic and chemical mechanisms should ultimately lead to a better and possibly predictive understanding of the enzymes' involvement in the detoxication of xenobiotics. Similarly, determining the action of glutathione S-transferase as a xenobiotic carrier protein will allow its role in the physical distribution of toxic materials in the cell to be defined.